Many investigators believe that the autonomic nervous system (ANS) may be involved in hyperactivity (HA) in children. The objectives of our studies are to investigate differences in autonomic functioning between HA and normal children by means of peripheral indicators such as skin temperature, and to assess the effects of the drugs on both autonomic activity and on task performance which depends on attention such as reaction time. The hypothesis that HA and normal children respond differently to stimulant drugs has been tested in a study of the effects of d-amphetamine on autonomic activity and attention in 6 to 13-year-old normal and HA boys. On the same protocol male adults have been tested for age differences in drug effects. Studies have been done on the acute and chronic effects of caffeine on these measures in boys and in normal men.